Gas species separation from mixtures represents an important industrial and economic process. In the natural gas production industry, for example, almost all raw (as-produced) natural gas is processed to remove various contaminants and non-valued gases before downstream utilization, such as introducing it as a product into a pipeline transportation system. For example, co-produced gases such as carbon dioxide and hydrogen disulfide, especially in combination with water, can heavily impact the value of as-produced natural gas. Production of unconventional gas sources such as shale plays and coal beds is increasing and driving a need for more efficient and affordable processing systems at more remote sites and with higher contaminant gas level processing capabilities. Contaminants in other types of gases can also be problematic and can impact their valuation, as well as the applicability of various industrial processes. For example, CO2 and contaminant capture from industrial flue gas, hydrogen purification and recovery processes, syngas production, and fuel cells represent non-limiting areas that can benefit from gas separation technology.
Separation membranes are commonly used for gas separation processes in a variety of industrial settings, including speciation of natural gas. Gas separation membranes are attractive for use in gas phase separation processes because they generally possess no or few moving parts, require low maintenance, exhibit low energy consumption, and possess exceptional reliability. However, many conventional membranes are not highly efficient, can be chemically unstable in certain instances and do not compete well with bulk non-membrane separation processes. For example, illustrative bulk carbon dioxide separation technologies can include cryogenic separation, pressure-temperature adsorption cycles, CO2 capture with amines, and the like. CO2 separation membranes, in contrast, can operate well at high CO2 concentrations, but can be less effective at modest H2S concentrations. Nevertheless, with proper process design, membrane-based gas separation processes can be used to simplify overall process design and be more convenient for deployment in remote field locations.
Specialized polymer membranes have been developed for use in specific gas separation applications. Examples include cellulose acetate membranes for CO2 separations in “sour gas” conditions, polyimide membranes, and polyamide membranes. Many different polymers are used in this regard, as different polymers have utility and affinity for use with different gas species, allowing certain gases to transit the membrane in preference to others. The transit mechanism can depend on specific interactions between gas and polymer molecules that affect gas dissolution and diffusion through the polymer. The polymer is generally chosen to enhance these interactions for the target gases and enhance the permeation rate of a desired gas over the permeation rate of an undesired gas, or vice versa. Generally, a membrane is considered to give an adequate separation of two gases from one another if the permeation ratio of the two gases is about 10:1 or above, although other permeation ratios can also be adequate depending on the intended application in which the gas will be used. Although widely used, existing polymer membranes can display inadequate performance for certain gas mixtures or not be applicable to certain types of process conditions. For example, chemical stability of the polymer membrane under certain process conditions can represent a concern.
A variety of other materials have also been developed for use in gas separation. Mesoporous and nanoporous inorganic materials that exhibit selective permeability of gas species include ceramic materials, nanoporous silicon, nanoporous metals, zeolite materials and zeolite-type materials. Materials such as zeolites and zeolite-type materials are molecular sieves which are capable of acting as sieves on a molecular scale and are characterized by uniformly sized pores of molecular dimension that can adsorb small molecules. Nonporous thin layers of metal can also exhibit selective adsorption and transport of gas or gases. For example, a thin platinum layer can absorb and transport hydrogen. Nanoporous carbon membranes and metal organic framework materials also can provide selective transport of gas species. In some cases, a membrane of these materials may be provided as composite membrane including a selective layer supported on a porous support. For example, zeolite or zeolite-type membranes may include a selective zeolite or zeolite-type membrane layer supported on a porous inorganic support (e.g. metal or ceramic).
In view of the foregoing, improved techniques for gas separation, particularly using membrane technology, would be of considerable benefit in the art. The present disclosure satisfies this need and provides related advantages as well.